Mineral fibers, such as glass fibers, are useful for insulation and structural products. Glass fibers for such products are typically made by feeding molten glass into a spinner, and centrifuging the fibers by rotating the spinner to form a downwardly moving cylindrical veil of glass fibers. Applied to the fibers are various organic coatings, particularly binders for binders connecting the mineral fibers to each other to form insulation or structural products. Glass fiber insulation products are typically bonded together by urea phenol/formaldehyde binder to form a spring-like matrix which can recover after compression during packaging of the product. Typical urea phenol/formaldehyde binders have a molecular weight of about 600 in the uncured state, and these binders are usually applied in an aqueous medium by spraying onto the glass fibers shortly after the fibers are formed.
One of the problems with applying aqueous organic binders of the prior an to cylindrical veils of mineral fibers is that a portion of the binder tends to evaporate prior to contact between the liquid binder drop and a mineral fiber in the veil. The evaporated binder material becomes a contaminant in the exhaust air stream of the process and must be cleaned up in order to avoid pollution problems. Also, the binder material on the mineral fibers tends to be sticky, requiring extensive cleaning of the fiber collection apparatus to prevent the build-up of clumps of glass fiber insulation material which can drop into the product and cause a product defect.
A recently developed process to apply higher molecular weight binders to glass fibers uses a first spinner to produce a downwardly moving veil of glass fibers and a second spinner, positioned within the veil, to form polymer fibers and to distribute them into contact with the glass fibers in the veil. This process produces a commingled insulation pack having some polymer fibers and some glass fibers having a polymer coating. This cofiberizing process is described in U.S. patent application Ser. No. 08/079,413, which is hereby incorporated by reference, and which was filed Jun. 23, 1993, naming Bakhshi et al. as inventors, and is assigned to the assignee of the present invention.
One of the problems with the cofiberizing approach to intermingling polymeric or organic material with glass fibers is that the polymeric material is exposed to a hostile environment. The polymer spinner is of necessity positioned directly beneath the glass spinner in order to have the polymer material intersecting the veil of glass fibers at a high enough level for effective commingling. The glass spinner is operated at nearly 2000.degree. F. and a considerable amount of heat is transferred via radiation, conduction and convection toward the polymer spinner and the polymer material within the spinner. Excessive heating of the polymer material causes degradation of the polymer. Even more troublesome is the problem of fires. If the polymeric material is exposed to air and elevated temperatures, a portion of the polymeric material will vaporize and the combustion process will commence. Burning polymeric material is an unacceptable side effect of the process. It would be advantageous for a cofiberizing process to be able to deliver the polymeric material to the spinner in a manner which minimizes the thermal degradation of the polymeric material, and which reduces the exposure of molten polymeric material to air to prevent combustion.